I’ve always known the word "oversight" to refer to an error that arose due to carelessness. I have however, repeatedly come across the word "oversight" used as the noun of "oversee”. I checked www.dictionary.com for the meaning of the word and this is what it says:

o·ver·sight –noun 1. an omission or error due to carelessness: My bank statement is full of oversights. 2. unintentional failure to notice or consider; lack of proper attention: Owing to my oversight, the letter was sent unsigned. 3. supervision; watchful care: a person responsible for the oversight of the organization.